A hardware or software setup that translates between two dissimilar protocols

2. Any mechanism for providing access to another system; for example, a router may the gateway to the Internet for LAN users.

Half-duplex Any device that can only send or receive data at any given moment. Most Ethernet transmissions are half-duplex.

Handshaking A procedure performed by modems, terminals, and computers to verify that communication has been correctly established.

Host A single device (usually a computer) on a TCP/IP network that has an IP address;

any device that can be the source or destination of a data packet. This may be a PC, a printer or server.

HOSTS file A static text file that resides on a computer and is used to resolve DNS host names to IP addresses. The HOSTS file is checked before the machine sends a name resolution request to a DNS name server. The HOSTS file has no file extension.

HTML (hypertext markup language) An ASCII-based script-like language for creating hypertext documents like those on the World Wide Web.

HTTP (hypertext transfer protocol) Extremely fast protocol used for network file transfers in the WWW environment.

HTTP over SSL (HTTPS) A secure form of HTTP, used commonly for Internet business transactions or any time where a secure connection is required.

Hub A hardware device that sits at the centre of a star topology network, providing a common point for the connection of network devices.

ICS (Internet connection sharing) A term used to describe the technique of enabling more than one computer to access the Internet simultaneously using a single Internet connection. When you use Internet sharing, you connect an entire LAN to the Internet using a single public IP address.

IEEE (the Institute of Electrical and Electronics Engineers) Institute of Electrical and Electronics Engineers. A professional association and standards body covering technical areas such as computer engineering, telecommunications, electric power, and consumer electronics amongst others. The IEEE Project 802 is the group within IEEE responsible for LAN technology standards.

Impedance The amount of resistance to an electrical signal on a wire. It is used as a relative measure of the amount of data a cable can handle.

Incremental backup A type of backup that backs up all files that have their archive bits turned on, which means they have been changed since the last backup. This type of backup turns the archive bits off after the files have been backed up.

Infrastructure mode Wireless networks running in infrastructure mode use one or more wireless access points to connect the wireless network nodes centrally. Wireless nodes cannot connect directly with each other.

Internal threats All the things that a network’s own users do to create problems on the network. Examples include accidental deletion of files, accidental damage to hardware devices or cabling, and abuse of rights and permissions.

Internet control message protocol (ICMP) ICMP messages consist of a single packet and are connectionless. ICMP packets determine connectivity between two hosts.

Internet protocol version 4 (IPv4) IPv4 addresses consist of four sets of numbers, each number being a value between 0 and 255, using a dot to separate the numbers. This is often called dotted decimal format. Examples include 192.168.0.1 and 81.176.19.164.

Internet protocol version 6 (IPv6) IPv6 addresses consist of eight sets of four

hexadecimal numbers, each number being a value between 0000 and FFFF, using a colon To separate the numbers. An example is EEDC:BA98:7654:3210:0800:200C:00CF:1234.

Intranet A private network inside a company or organisation that uses the same kinds of software and services you find on the Internet, but that is only for internal use.

I/O (input/output) A general term for reading and writing data to a computer. The term input includes data from a keyboard, pointing device (such as a mouse), and a file from a disk. Output includes writing information to a disk, viewing it on a monitor and printing it to a printer.

I/O device Pieces of hardware that enable a user to move data into or out of the computer, such as a mouse or a keyboard.

IP (Internet protocol) The Internet standard protocol that provides a common layer over dissimilar networks used to move packets among host computers and through gateways if necessary. IP is part of the TCP/IP protocol suite.

IP address The numeric address of a computer connected to a TCP/IP network, such as the Internet. The IP address is made up of four octets of 8-bit binary numbers that are translated by the computer into their shorthand numeric values; for

example,11000000.10101000.00000100.00011010 = 192.168.4.26. IP addresses must be matched with a valid subnet mask, which identifies the part of the IP address that is the network ID and the part that is the host ID.

IPCONFIG A command-line utility for Windows PCs that displays the current TCP/IP configuration of the machine; similar to Unix/Linux’s IFCONFIG and the graphical WINIPCFG available in Windows 9x and Windows XP.

IPSec (IP Security) A group of protocols used to encrypt IP packets. IPSec is most commonly seen on VPNs. See VPN (virtual private network).

IPX/SPX (Internetwork Packet Exchange/Sequence Packet Exchange) Protocol suite developed by Novell, primarily for supporting Novell NetWare-based networks.

ISDN (Integrated Services Digital Network) The standard that defines a digital method for communications to replace the current analogue telephone system. ISDN is superior to analogue dial-up telephone line connections because it supports up to 128 Kbps transfer rate for sending information from computer to computer. It also allows data and voice to share a common phone line.

Network Concepts: Advanced COLEG

ISP (Internet service provider) A company that provides access to the Internet in some form, usually for a fee.

Kbps (kilobits per second) Data transfer rate of 1000 bps.

Kerberos An authentication standard designed to allow different operating systems and applications to authenticate each other.

KHz (kilohertz) A unit of measure that equals a frequency of one thousand cycles per second.

LAN (local area network) A group of PCs connected together via cabling, radio, or infrared, and using this connectivity to share resources such as printers and mass storage.

Layer A grouping of related tasks involving the transfer of information, related to a particular level of the OSI Reference Model, for example, Physical layer, Data Link layer.

LMHOSTS file A static text file that resides on a computer and is used to resolve NetBIOS names to IP addresses. The LMHOSTS file is checked before the machine sends a name resolution request to a WINS name server. The LMHOSTS file has no extension.

Localhost An alias for the loopback address of 127.0.0.1, referring to the current machine.

Logical address An address that describes both a specific network and a specific machine on that network.

Loopback address Sometimes called the localhost, the loopback address is a reserved IP address used for internal testing: 127.0.0.1.

MAC (media access control) Unique 48-bit address assigned to each network card. IEEE assigns blocks of possible addresses to various NIC manufacturers to help ensure that each address is unique.

Mbps (Megabits per second) Data transfer rate of a million bits per second.

Mesh topology Each computer has a dedicated connection to every other computer in a network. Used in networks that have to have redundancy built in.

MHz (megahertz) A unit of measure that equals a frequency of 1 million cycles per second.

Mirroring Also called drive mirroring. Reading and writing data at the same time to two drives for fault-tolerance purposes. RAID level 1.

Modem (modulator/demodulator) A device that converts both digital bit streams into analogue signals (modulation) and incoming analogue signals back into digital signals (demodulation). The antilog communications channel is typically a telephone line and the analogue signals are typically sounds.

MSCONFIG A utility found in Windows that enables a user to configure a system’s boot files and critical system files.

Name resolution A method that enables one computer on the network to locate another and establish a session. All network protocols perform name resolution in one of two ways:

by broadcasting or by providing some form of name server.

Name server A computer whose job is to know the name of every other computer on the NAT (network address translation) NAT works hand-in-hand with DHCP to mask the IP address of network clients behind a single public IP address. NAT devices (either

dedicated hardware devices such as routers, or a PC with two NICs running the software NAT service) have two interfaces: one that connects to the Internet via an ISP-supplied IP address, and another that connects to the LAN. The NAT service translates the IP

addresses and TCP/UDP port numbers of data packets forwarded from the LAN interface from an address in the private IP address range to the public IP address. NAT enables multiple network clients to share a single Internet connection, and provides a level of firewall-like security.

NetBEUI (NetBIOS extended user interface) NetBEUI is an extended version of the NetBIOS protocol that operates at the Transport layer of the OSI model. NetBEUI has been overshadowed by other protocols, such as IPX/SPX, mainly because NetBEUI is not routable and therefore unsuitable for connecting to the Internet. From Windows XP

onwards, Microsoft is phasing support for NetBEUI out of its products.

NetBIOS (network basic input/output system) The NetBIOS protocol creates and manages connections based on the names of the computers involved. NetBIOS operates at the Session layer of the OSI model.

NetBIOS name A computer name that identifies both the specific machine and the functions that machine performs. A NetBIOS name consists of 16 characters: the first 15 are an alphanumeric name, and the 16th is a special suffix that identifies the role the machine plays.

Network A collection of two or more computers interconnected by telephone lines, coaxial cables, satellite links, radio, and/or some other communication technique. A computer network is a group of computers that are connected together and communicate with one another for a common purpose. Computer networks support people in organisations to share information and allow an addition form of communication

Network interface card (NIC) A hardware device that connects the PC to a network. NICs come as internal component cards that install onto the PC’s motherboard, or as external devices the use the PC’s USB or PC card ports. NICs may have connections for coaxial, STP, UTP, fibre optic cabling, 802.11x or bluetooth-based wireless technology.

Network layer See OSI Reference Model.

Network topology 1. The physical structures that connect PCs to each other, including cabling, routers, hubs, patch panels, and other pieces of hardware. 2. The logical organisation of a network, such as domains and workgroups.

NFS (Network File System) A distributed file system that allows a computer to access files and directories located on remote computers over a network, as if they were on its local disks.

Normal backup A full backup of every selected file on a system. This type of backup turns off the archive bit after the backup.

NOS (network operating system) An operating system that provides basic file and supervisory services over a network. While each computer attached to the network has its

Network Concepts: Advanced COLEG

own operating system, the NOS describes which actions are allowed by each user and coordinates distribution of networked files to the users who request them.

Novell NetWare A popular and powerful NOS that provides network services ranging from simple file storage and sharing to World Wide Web, email, VPN, and other services. Novell NetWare is the only NOS that adheres to the strict definition of client/server.

NWLink Also known as IPX/SPX compatible protocol, this is Microsoft’s implementation of IPX/SPX. See also IPX/SPX (internetwork packet exchange/sequence packet exchange).

Ohm Electrical unit of resistance. The value of resistance through which a potential of one volt will maintain a current of one ampere.

OSI (Open Systems Interconnection) An international standard suite of protocols defined by the International Organisation for Standardisation (ISO) that implements the OSI Reference Model for network communications between computers.

OSI Reference Model An architecture model based on the OSI protocol suite, which defines and standardizes the flow of data between computers. The seven layers of the OSI model are as follows:

Layer 1: The Physical layer defines hardware connections and turns binary into